The invention relates to a circular knitting machine with a replaceable needle cylinder, containing a support ring with a supporting surface for the needle cylinder, at least one attachment projecting axially above this and a means to facilitate replacement of the needle cylinder, which has lifting parts acting on the needle cylinder, by means of which the needle cylinder is selectively adjustable into an operating position, in which its lower side lies on the supporting surface and is arranged below an upper edge of the attachment, and into a mounting position, in which its underside is held in a raised position by the lifting parts, so that it is arranged to be at least flush with the upper edge of the attachment. Further, the invention relates to a needle cylinder which can be used in such a knitting machine.
Circular knitting machines with a replaceable needle cylinder have been known for a long time (patent DE 177 577 A). When a circular knitting machine has only one needle cylinder, its insertion and removal is relatively simple. In this case, the insertion and removal can be for the purposes of repair and maintenance as well as for the purpose of operating the same circular knitting machine with needle cylinders of different gauge and/or different diameters. Since the area above the needle cylinder is substantially free, the needle cylinder and possibly the associated support rings only need to be lifted out of the machine frame or inserted into this from the top.
However, the insertion and removal of a needle cylinder from the top is not readily possible if the circular knitting machine additionally has a structural part arranged above the needle cylinder, e.g. a dial or a thread changing device, since a removal of such structural parts would render a virtually complete disassembly of the circular knitting machine necessary. Therefore, for these cases it is already known (patent documents EP 0 413 608 A1, EP 0 436 313 A1) to provide an arrangement, by means of which the relative position between the needle cylinder and the structural part is adjustable in the direction of the needle cylinder axis such that the needle cylinder can be inserted or removed in a direction running vertically to the needle cylinder axis, i.e. selectively with or without the said structural part. However, such an insertion or removal of the needle cylinder is still problematic even when the structural part is sufficiently raised. A reason for this is that the needle cylinder is generally arranged with its lower edge in a recess of the cylinder support ring and/or is provided with additional centring means, which render it necessary to significantly raise the needle cylinder during removal and lower the needle cylinder accordingly during insertion. These movements must be performed manually by the operating personnel concerned with the replacement. As a result, removal and insertion measures are made particularly difficult when the needle cylinder is additionally subject to the weight of a structureal part positioned on it, e.g. a dial.
To prevent these disadvantages, it is known (DE 195 33 844 A1) to generally remove the needle cylinder together with the dial positioned on it and, if this concerns large circular knitting machines, detachably mount the dial on a dial support. Prior to the radial removal of the needle cylinder and the dial, this dial support is lowered down through the needle cylinder by means of a special hoisting device to such a depth that its upper edge comes to lie below the lower edge of the needle cylinder and as a result cannot hinder the radial removal of the needle cylinder.
Finally, a circular knitting machine of the aforementioned type is known (DE 196 53 761), which has means for adjusting the needle cylinder in axial direction in such a way that the needle cylinder can be selectively adjusted into a usual operating position or into a raised mounting position enabling the insertion and removal. These means comprise either lifting jacks, which can be mounted in the support ring of the needle cylinder and can be placed against the underside of the needle cylinder, or lifting rails, which can be mounted between the needle cylinder or the support ring and have non-round cross-sections. While the application of the lifting jacks makes comparatively complicated operations necessary during replacement of a needle cylinder, the replacement of a needle cylinder with the aid of lifting rails is barely possible for a single operator to perform because of the high forces that have to be applied. This applies in particular where comparatively heavy needle cylinders of large circular knitting machines are concerned and dials or other structural parts must be removed together with the needle cylinders. Apart from this, the replacement of a needle cylinder requires a plurality of working steps, as in the case of other known circular knitting machines, and this makes the replacement operation additionally difficult.